Simplify the following expression: $k = \dfrac{15r^2 + 5r}{10sr + 5r} - \dfrac{5r^2 + 5r}{10sr + 5r}$ You can assume $r,s,t \neq 0$.
Explanation: Since the expressions have the same denominator we simply combine the numerators: $k = \dfrac{15r^2 + 5r - (5r^2 + 5r)}{10sr + 5r}$ $k = \dfrac{10r^2}{10sr + 5r}$ The numerator and denominator have a common factor of $5r$, so we can simplify $k = \dfrac{2r}{2s + 1}$